Similar to batteries, fuel cells function to produce electricity through chemical reactions. Rather than storing reactants as batteries do, fuel cells are operated by continuously supplying reactants to the cell. In a typical fuel cell, hydrogen gas acts as one reactant and oxygen as the other, with the two reacting at electrodes to form water molecules and releasing energy in the form of direct current electricity. The apparatus and process may produce electricity continuously as long as hydrogen and oxygen are provided. While oxygen may either be stored or provided from the air, hydrogen gas may be generated from other compounds through controlled chemical reactions rather than storing hydrogen, which may need to be compressed or cryogenically cooled. As fuel cell technology evolves, so do the means by which hydrogen gas is generated for application with fuel cells.
One means by which hydrogen gas is generated is through reactive chemical hydrides. This process involves chemically generating hydrogen gas from dry, highly reactive solids by reacting them with water. Chemicals especially suitable for this process are lithium hydride, calcium hydride, lithium aluminum hydride, sodium borohydride and combinations thereof, each of which is capable of releasing plentiful quantities of hydrogen.
It has been found that the reaction products from the chemical hydride and liquid water typically form a cake or pasty substance which interferes with further reaction of the reactive chemical with the liquid water or acid. Furthermore, the reaction of chemical hydrides with liquid are difficult to control, and generally results in the production of much more hydrogen gas than needed to power small electronic devices.
In order to combat this problem, methods have been introduced wherein a hydrogen fuel can be reacted with gaseous water vapor, instead of liquid water. In many hydrogen generator designs, an elaborate power generator system is used in order to regulate the quantity of water vapor that reacts with the chemical fuel and to regulate the reaction rate of water vapor with the chemical fuel.